1. Technical Field
The present invention relates to a multiple access communication system and a data transceiver used in a broadband access network or the like.
2. Related Art
Broadband access networks such as cable modems using cable television lines or Fixed Wireless Access (FWA) using fixed radio channels have been provided even in ordinary households to implement high speed internet access. Cable modems and FWA are described in detail in, for example, Nikkei Communication, No. 316, April 2000. Those broadband access networks nearly all use multiple access lines where a number of users share the same frequency band as an uplink, in order to reduce costs. With multiple access type lines, each slave station is connected to a master station through shared media for sharing the same frequency band with other slave stations and a transmission order between slave stations is controlled by master station multiple access control.
In order to synchronize time between the master station and all of the slave stations, the master station distributes a time synchronization packet via a broadcast channel. In this type of multiple access communication system, in order to use the uplink efficiently, each slave station concatenates a plurality of uplink transmission data packets to transmit them. Also, the slave stations separately manage transmission data itself and state information representing the state of the transmission data. When a slave station sets a control flag within the state information to unchangeable, a MAC (media access control) controller automatically transmits a corresponding transmission data body to the uplink. When concatenating and transmitting, the slave station sets a concatenated transmission flag in the state information, and the MAC controller consecutively concatenates all transmission data bodies having a concatenated transmission flag set and automatically transmits them to the uplink.
When transmitting communication data, a conventional multiple access communications system adds additional information to the communication data to be transmitted. In the case of concatenating a plurality of transmission data, additional information for indicating that there is concatenated data is further added for transmission. By doing this, if the size of the additional information becomes large compared to the size of the transmission data, the concatenating of a plurality of transmission data for transmission suffers from a first problem that conversely the utilization rate of the multiple access lines is degraded.
Also, when a slave station concatenates and transmits a plurality of transmission data, the uplink is occupied for a long period of time so there is a second problem that the length of time that other slave stations must wait until transmitting transmission data is increased.
According to a conventional multiple access communication system, generation of transmission data and transmission to the multiple access line is asynchronous. Accordingly, there is developed a third problem that a delay in transmission data, which is required in real time, is increased.
Since transmit packets in a transmission buffer are transmitted automatically one by one in order to concatenate and transmit transmission data there is a fourth problem that it is necessary to have completed concatenating processing by the time transmission data is put into the transmission buffer.
The uplink control information and uplink user data make shared use of the same transmission buffer, and a slave station sequentially performs transmission from header transmission data in the transmission buffer. Accordingly, there is a fifth problem that the uplink control information is not given priority over the uplink user data when performing transmission.
In the case of concatenating a plurality of packets having a fixed information length, Japanese Patent Application Unexamined Publication No. 61-33054 discloses a packet transmitting/receiving system where a start block is added to the leading end of the concatenated packets and an end block is added to the trailing end thereof. However, this prior art is applicable to a fixed-length packet transmitting/receiving system.